Haemophilus ducreyi is the etiologic agent of the genital ulcer disease chancroid. All H. ducreyi strains tested express an outer membrane protein designated PAL (peptidoglycan associated lipoprotein) that has extensive homology with protein 6 (P6) of Haemophilus influenzae influenzae. P6 is receiving intensive syudy as a vaccine candidate to prevent H. influenzae infections,and is in phase II clinical trials. P6 and the 18K OMP share several features, including conservation within each species, surface exposed, and antigenic stabillty. The purpose of this study is to test the hypothesis that a PAL mutant is impaired in its ability to infect human skin when compared to its isogenic parent. To test this hypothesis, we will compare the ability of the parent and the mutant to cause experimental infection in human subject. These studies will establish whether expression of PAL is required for H.ducreyi to cause pustules, and may provide a rationale to test the P6 vaccine for efficacy against H. ducreyi.